1. Field of the Invention
The present invention relates to a process for forming hydrogen-containing gas mixtures by catalytic partial oxidation of hydrocarbon mixtures containing a heavy residual oil.
2. Description of Prior Arts
As the process for the gasification of natural gases and light hydrocarbons such as petroleum fractions of up to naphtha, there are known a partial oxidation process using a nickel catalyst, a steam reforming process and a non-catalytic partial oxidation process. For the gasification of hydrocarbon mixtures containing a heavy residual oil, such as crude oils, atmospheric pressure distillation residual oils and vacuum distillation residual oils, only the partial oxidation process not using a catalyst is worked on an industrial scale, and the catalytic steam reforming process or the catalytic partial oxidation process has not yet been industrialized.
The process for the gasification of a hydrocarbon mixture containing a heavy residual oil by non-catalytic partial oxidation has already been utilized for production of synthesis gases such as ammonia and methanol synthesis gases. With recent tightening of regulations for the maximum permissible SO.sub.2 concentration in exhausted gases for prevention of environmental pollution, application of this partial oxidation process to desulfurization gasification for obtaining clean fuel gases by removing from the formed gas mixture sulfur which is converted to hydrogen sulfide at the gasification has been tried in the art.
This non-catalytic partial oxidation process comprises adding steam to a heavy residual oil and partially burning the heavy oil at a temperature higher than about 1,300.degree. C. by oxygen, oxygen-rich air or air to thereby gasify the heavy residual oil. Since a high temperature is required in that process, oxygen must be used in a large quantity when oxygen is used. Therefore, that process is defective in that an expensive oxygen supply apparatus having a large capacity must be provided. When air is used, a large quantity of compression power must be supplied to the air compressor.
Heat is recovered from a high temperature gas formed by the gasification by generating steam by heat exchange, but since carbon is present in the gas and the gas pressure is high, the expenses of equipment for performing this heat exchange become tremendous.
Further, in order to obtain a high temperature, a larger proportion of the starting oil must be burnt. Therefore, the yield of the formed gas is reduced although the quantity of steam obtained by heat recovery increases.
In the fuel gas or the synthesis gas production processes in which it is a primary object to obtain the formed gas, reduction of the yield of the formed gas results in reduction of the productivity of the process. Even if all of steam, electric power and fuel gas are intended products, when the yield of the fuel gas is low, the range of controlling the production ratio of steam, electric power and fuel gas is narrowed and the flexibility of the process becomes small.
If the yield of the fuel gas is high, it is possible to generate electric power by using the steam formed by employing the fuel gas for a boiler. In other words, the ratio of the outputs of steam, electric power and fuel gas can be selected optionally to some extent.
Furthermore, since the reaction temperature is high in the above-mentioned non-catalytic partial oxidation process, the spray nozzle for feeding the starting oil to the reactor is extremely damaged, and replacement of nozzles must be performed frequently, resulting in a reduction of the operation efficiency. Moreover, because of the high reaction temperature, the refractory bricks constituting the inner wall of the reactor are damaged by heavy metals contained in the heavy residual oil.
Still in addition, in the above non-catalytic partial oxidation process, formation of carbon in an amount of 2 to 4% cannot be obviated, and therefore, equipment expenses must be additionally increased for removal of the formed carbon and recycle of it to the feed stock and the operation efficiency is lowered accordingly.
In order to overcome the foregoing defects involved in the conventional process, it is desired to perform gasification at lower temperatures by the catalytic partial oxidation and to reduce formation of carbon.
It is known that catalysts comprising as a main active component an alkali metal such as Na and K or an alkaline earth metal such as Be, Mg, Ca and Sr are effective for such catalytic gasification.
As the process using a catalyst of this type, there are ordinarily considered a process using a fluidized bed reactor and a process using a fixed bed reactor. When a fixed catalyst bed reactor is used for gasification of a hydrocarbon mixture containing a heavy residual oil, the catalyst bed is clogged in a short time by carbon formed by the reaction and continuation of the operation becomes impossible. Therefore, efforts have heretofore been mainly made to develop a process using a fluidized bed reactor.
The fluidized bed is not adversely affected directly by formation of carbon, but the process using a fluidized bed is defective in that complex techniques must be developed for prevention of wearing of catalyst particles, facilitation of supply and withdrawal of the catalyst, increase of the operation scale and elevation of the operation pressure.
If the defect of clogging by deposited carbon is eliminated, the process using a reactor of the fixed bed type will apparently be advantageous because the structure of the reactor is simple and the operation efficiency is high.